Aircraft: SMALL TRANSPORT
Phase of flight: Climb
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy

I am currently a CPC-IT (Controller In Training) and was training on radar. I had just taken the position from a previous controller and saw that Aircraft X was departing off SFF on a heading of 300 restricted at or below 3500 feet(this is a built in procedure for VFR aircraft coming off SFF). I was briefed that Aircraft Y was cleared on the RNAV Z RWY 21 approach and had been switched to the tower. I recognized that the two aircraft were going to be a conflict and was trying to formulate a solution. Aircraft Y was descending out of approximately 4500 feet when Aircraft X checked on level at 3500 feet. At this point the two aircraft were pointed right at each other approximately 3 miles apart. I knew aircraft on the RNAV Z RWY 21 approach were allowed to descend to 3500 which is the exact altitude that Aircraft X was restricted at. When Aircraft X checked on I told him altitude your discretion and to proceed on course; followed by a traffic call. My initial plan was to have Aircraft X climb above the descending Aircraft Y; then issue a northerly heading if necessary. My instructor keyed over me at that point; gave a traffic alert and told Aircraft X to fly northbound. The tower then called saying Aircraft Y was responding to a TCAS alert and was coming back to radar for resequencing. Aircraft X continued on course below Aircraft Y and the session continued without further incident. Foremost; it was poor control judgment on my part to not issue an immediate turn to Aircraft X and to think that an altitude swap alone was going to resolve the situation. I was slow to see how quickly the situation was developing and should have been quicker to react. However; I do think that the letter of agreement (LOA) pertaining to automatic VFR releases between SFF and GEG is flawed. The procedure calls for all VFR aircraft whose departure routes will take them towards GEG Class C surface area to either fly heading 300 at or below 3500 feet or remain south of the interstate at or below 3500 feet. My two main concerns with this procedure relate to aircraft separation and vectors below the minimum vectoring altitude. VFR aircraft departing SFF on a heading of 300 at or below 3500 points them directly at GEG's final. Typically aircraft on the visual approach to RWY 21 and other approach procedures pass over these VFR aircraft at 4000. However; outside of issuing an immediate control instruction to avoid a conflict; there is no ensured separation with this procedure. This lack of separation can also happen with VFR aircraft departing south of the interstate at or below 3500 feet. It is especially concerning to me that aircraft on the RNAV Z RWY 21 approach can descend to 3500 feet on the base turn; the exact altitude that a VFR aircraft coming off of SFF can be at.I also think the LOA is contradictory to the 7110.65 relating to vectors below the MVA (Minimum Vectoring Altitude). In the 7110.65 per 5-6-1 it makes it very clear that a VFR aircraft cannot be assigned a heading and altitude below the MVA (with certain exceptions that either don't apply in this case or have not been made clear to me). All of our MVAs in the area are above 3500 ft MSL which make me unsure of how this LOA is meeting the 7110.65 requirement. This incident definitely drove home the point that imminent traffic situations can develop very quickly and at any time. In future situations I will take more evasive action and be more vigilant to avoid making a similar mistake. I think departing VFR aircraft either to the NE or SE would be a better procedure for SFF. However; I know there is higher terrain east of SFF so this might not be possible. The other idea would be for SFF to call for VFR releases. I definitely think this procedure should be revisited to avoid conflicts with future aircraft. An Air Traffic Controller Trainee reported failing to take sufficient action to keep a VFR aircraft away from an IFR aircraft executing an approach to an airport. The Trainee Controller mistakenly believed he could not vector the VFR aircraft below the MVA.